I'd say no on the KOs. They make good display pieces, but there's little heart or effort shown in it. I don't exactly mind KOs being made at really really low prices, as it can benefit someone who can't make up the cash to buy an official one. As already said, I'm not going to look down on or shame someone for buying a KO if they absolutely need to with their current financial sitatuation, as I sort of understand, not getting much money myself, still an adolescent. However, you may be able to get a loose placeholder, as Gok said, for a lower price, which is nice.
From the price you can usually tell it's a KO, which gives you some benefit.
However, what I hate and absolutely despise, is the selling of KOs at exorbitant prices, being pushed as the real thing. Honestly, from scouting eBay for various G1 figures, some MIB or MISB toys, such as Shockwave, you can tell when something's a knockoff, being below about $120, which is way too much for a KO and too low for the real thing, usually.
You see, MIB and MISB G1 figures usually command EXTRA high prices, well into $500 in some cases, which I honestly do not see as worth it anyway. The thing is, some people put KOs up at these same extra high prices, which can fool someone already well aware of the usual prices for KOs and legitimate figures, thinking that the high price must be indicative of it being totally legit.
This is why I'd never go to eBay for G1 figures unless they are loose and complete from a trusted source, as you can never be too sure on what people can do to mess around with you. I personally buy reissue toys of G1 figures anyway, unless that figure has not being reissued, in which I'd hope for HasTak do make one or look at some trusted sources, such as Transformerland, to find what I'm looking for.
I'm not exactly the best one in terms of experience, but this is just my 2c.